devicemapper: retry remove even for subLVs

devicemapper: retry remove even for subLVs

With older systems and udevs we don't have control over scanning of lvm2
internal devices - so far we set retry-removal only for top-level LVs,
but in occasional cases udev can be 'fast enough' to open device for
scanning and prevent removal of such device from DM table.

So to combat this case - try to pass 'retry' flag also for removal of
internal device so see how many races can go away with this simple
patch.

Note: patch is applied only to internal version of libdm so the external
API remains working in the old way for now.